[9] In 2007 he enjoyed a successful season and scored fifteen wins, ending up second in number of victories behind ProTour sprinter Alessandro Petacchi.

[11] Boasson Hagen began the 2008 season with a fifth place in the prologue of Tour of California, ahead of established time trial specialists like David Millar and Gustav Larsson.

He later won the concluding individual time trial of Critérium International ahead of teammate Tony Martin and the Grand Prix de Denain.

Boasson Hagen lost any chance of overall victory but made up by winning the following stage in Brussels by passing Jimmy Engoulvent in the final fifteen meters of the race.

In the Tour de Pologne he won the fourth and sixth stages to finish third overall, and secure Norway ten riders in the upcoming UCI Road World Championships.

Hagen also won his first stage race in 2009, the Eneco Tour, confirming his huge talent, and rising to third overall in the world ranking in August.

After months of rumours, it was official on 10 September 2009 that Boasson Hagen would be joining Team Sky from the 2010 season, along with fellow Norwegians Lars Petter Nordhaug and Kurt Asle Arvesen.

After an impressive effort and stage win in the opening team time trial, Boasson Hagen secured 3rd and 6th-place finishes as his best results.

[16] He won the Norwegian National Time Trial Championships for the fifth year running in June, but then contracted an illness that put his Tour de France in doubt.

[19][20] Boasson Hagen finished second to compatriot Thor Hushovd on stage sixteen after the pair were in a three-man breakaway with Ryder Hesjedal.

[23] In August, Boasson Hagen took a clean sweep of the jerseys at the Eneco Tour, winning the event overall, as well as the points and young riders competitions, and finishing first on the final stage.

He broke away from the bunch with a little more than two kilometers to go, caught and dropped the remaining man in front, Rui Costa (Movistar Team) on the last uphill section and descended to the finish solo.

[27] Boasson Hagen began the season with the stated ambition of winning one of the Spring classics,[28] but failed to attain any notable results.

[31] He was also named in the startlist for the Tour de France that year but on stage 12 he broke his collarbone in a huge crash ten kilometers from the finish line and was forced to abandon the race.

In the final kilometers of the UCI Road World Championships, Boasson Hagen refused to cooperate with Greg van Avermaet to close the 10-second gap to later winner Peter Sagan.

The most likely reason for Boasson Hagen not to put an effort in the chase was his fellow countryman and sprinter Alexander Kristoff who was in the main peloton just seconds behind the duo.

Boasson Hagen soloed to victory on stage 19 of the Tour de France, successfully attacking from the breakaway in the final few kilometres.

[37] In 2019, Boasson Hagen was the only rider on Team Dimension Data's roster to take a victory in a World Tour race, winning stage 1 of the Critérium du Dauphiné.